I recently heard a health professional make some odd comments about monosodium glutamate (MSG), comments such as “we’re supposed to avoid that” and “it’s supposed to be bad for us.” I asked her if she knew what it was. She confessed, “not really.” I loved her honesty as much as I worried about her sharing myths about MSG with patients and clients.
The truth – and it’s an indisputable truth – is that you can’t avoid glutamate, the “G” in MSG. Moreover, you don’t have to and you wouldn’t even want to if you could. It’s too important for our gut health, our digestion, and our taste buds. You’d also have to stop eating all protein foods, because glutamate is the most abundant amino acid in protein. It makes up about 20% of the amino acids in most high-quality proteins, whether they occur in animals or plants.
We should thank Mother Nature for glutamate every time we eat. Glutamate is what gives foods their “umami” taste. It’s responsible for this fifth taste (the others are bitter, sweet, salty, and sour) and it’s what makes some foods so tasty, foods like parmesan cheese, tomatoes, mushrooms and on and on.
You might think that all the glutamate, and the comparatively tiny amount we might get from MSG, we get from protein ends up in our bloodstream but it doesn’t. Our blood levels of all the amino acids we eat are kept very stable throughout the day, no matter how much of them we eat. With glutamate, the vast majority of it – over 98% — stays right in the gut, never even making it to the bloodstream.
There’s a reason: glutamate is involved in our digestive process. It’s complex, so I’ll cut to the chase: the body needs to constantly keep the right balance of amino acids in our blood, so it needs to know how much we’re eating. We have glutamate receptors on our tongues, probably to allow us to sense the presence of protein, given the amount of glutamate in all proteins. These “umami” receptors send the message to the brain that protein, not just glutamate, has arrived in our mouths. Sensing the umami taste starts this “brain phase” of digestion and it stimulates a desire for food intake and eventually the digestion and absorption of all nutrients.
Influence of Glutamate on Appetite and Weight
The influence of glutamate on appetite and digestion has been studied and reviewed. (Torii, et al.) Much of the appetite research uses rats because most research involving brains can’t be done on humans, and studies using rats have been a standard and excellent model for decades.
You may have heard about MSG being “linked” with weight gain. This I don’t understand, because not only did this study (Brosnan et al.) show that dietary MSG never makes it across the blood-brain barrier (it is broken apart, and virtually all the glutamate is used by cells in the gut lining for energy), a review (Tsurugizawa et al.) of the research found that the glutamate actually causes our bodies to increase heat production (technical term: thermogenesis) during eating, effectively helping raise our metabolic rate a bit.
Here’s what I find so fascinating: even though glutamate doesn’t make it to the brain, its presence makes itself known to the brain through various receptors, starting in the mouth. This review also pointed out that rats fed a chronically high-fat, high sugar diet and given a choice between water and a water solution containing 1% MSG vastly preferred the MSG solution (probably tastier) but in doing so they also avoided becoming obese.
Now, no one is suggesting that MSG be used as a tool for controlling calories or weight. But the role of glutamate in the digestive process, including signaling the presence of protein and possibly satiation, is intriguing and should not be dismissed. For those still wanting to avoid MSG, don’t be troubled – it only accounts for a tiny fraction of 1% of the glutamate people eat anyway. But there is certainly reason to appreciate the role glutamate plays in our food and welcome the presence of more “umami”.
As an added bonus, MSG gram for gram, contains about 62% less sodium than table salt. When cooking, swapping out about a quarter of the salt for an equal amount of MSG might make food taste better and also lower its sodium. Just a little win-win there, all courtesy of glutamate.
- Torii K, Uneyama H, and Nakamura E. Physiological roles of dietary glutamate signaling via gut–brain axis due to efﬁcient digestion and absorption. J Gastroenterol (2013) 48:442–451. DOI 10.1007/s00535-013-0778-1
- Brosnan JT, Drewnowski A, and Friedman MI. Is there a relationship between dietary MSG obesity in animals or humans? Amino Acids. 2014 Sep;46(9):2075-87. doi: 10.1007/s00726-014-1771-6
- Tsurugizawa T, Uneyama H, and Torii K. Brain amino acid sensing. Diabetes Obes Metab. 2014 Sep;16 Suppl 1:41-8. doi: 10.1111/dom.12336.